Galaxy Evolution, Cosmology and Dark Energy

How do galaxies evolve and what is dark energy?

Our Universe is expanding, and we have recently discovered that this expansion is accelerating. Scientists are still trying to understand why this is happening, with theories such as a force known as “dark energy” being put forward. The detection of this acceleration won the Nobel prize for physics in 2011.

This mysterious acceleration however, is still one of the most fundamental mysteries of modern science and also one of the key questions the SKA will try to address. One of the main science goals of the SKA is to investigate why this acceleration is taking place, by looking at the distribution of the most basic element, Hydrogen, throughout the cosmos. The SKA’s unrivalled sensitivity will be able to track young, newly forming galaxies at the edge of the known Universe, and by mapping the distribution of Hydrogen, help us unravel this key mystery, and understand more how the earliest galaxies evolved.

Hydrogen is the most abundant element in the Universe and is the raw material from which stars form.

Over 70% of our Sun is Hydrogen, and as a radio source, the Sun is one of the brightest objects not only in the visible sky, but also in the radio.

Since then, hydrogen gas has been found in tens of thousands of galaxies, most of which are relatively near to the Milky Way. Generally, astronomers find that spiral galaxies, like our Milky Way Galaxy, and irregular galaxies, like the Magellanic Clouds, often contain large amounts of hydrogen gas. These galaxies also form stars and astronomers believe that hydrogen gas provides the raw fuel for star formation.

Aside from dark energy, this mysterious force thought to be causing the acceleration of the expansion in the Universe, there is also Dark Matter, which astronomers believe makes up a large fraction of all matter in the Universe. The study of this came about after anomalies were found in the rotation rates and masses of galaxies, based on their visible characteristics and the values derived from observation.

The SKA will revolutionise our study of how galaxies form and transform their gas into stars by detecting hydrogen gas in surveys which make encompass as many as a billion galaxies, at distances much greater than is possible to detect today.